Flowable dry particles containing at least one oleophilic substance as the active ingredient present in a matrix of at least one carrier material and a coating are known. Their maximum content of oleophilic substance as the active ingredient has been 50 wt. %.
One process for the manufacture of such particles is described, for example, in German Patent 10 35 319 and in the corresponding U.S. Pat. No. 2,756,177, where a dispersion of an oily vitamin as the active ingredient is sprayed into a large excess of a starch powder having a water content below 8%, whereby the dry starch powder catches the spray particles and the spray particles remove an amount of water such that they solidify and are simultaneously coated with starch powder. A serious disadvantage of these particles is that about 15% of the amount of starch adheres to their surface and therefore the particles contain only a relatively low amount of active ingredient.
According to a similar process described in U.S. Pat. No. 3,445,563 the starch is replaced by a mixture of inorganic substances which absorb water and which do not absorb water in order to eliminate the danger of explosion which emanates from the finely divided starch. A 20-fold excess of the catch powder is necessary in order to obtain optimal results. As a water-absorbing component of the catch powder there is named, inter alia, calcium silicate, especially calcium aluminium silicate, as the oil-soluble active ingredient there is mentioned vitamin A and vitamin D. In the case of an active ingredient activity lying between 245 000 and 532 000 I.U./g the particles obtained contain up to 19% catch powder as the coating.
Further, a process has become known from European Patent Application 0074050 which is useful for the manufacture of dry, free-flowing powders of readily oxidizable substances, such as the vitamins or carotenoids, which are coated with a colloid. The process comprises dispersing these substances in an aqueous solution of a film-forming colloid, with the colloid being the homogeneous phase. With the addition of one or more substances from the group of mono-, di- or polysaccharides the dispersion is sprayed into a spray tower with the co-use of a spray aid agent and the sprayed particles are collected in a fluidized bed. Thereby, a hydrophobic silicic acid or a metal salt of a higher fatty acid or a mixture with silicic acid in a 0.02- to 0.15-fold amount by weight based on the dispersion is introduced as the spray aid agent above the fluidized bed with homogeneous distribution in the spray area at temperatures at which a solidification of the colloid of the sprayed particles does not yet occur. The particles loaded with aid agent, the colloid mass of which is essentially not gelled, is collected in a fluidized bed and the particles are dried in the fluidized bed in a manner known per se.
Although in this process only a thin, hydrophobic film of the spray aid agent is produced, the particles formed during the spraying are sufficiently stabilized to prevent an agglomeration of the particles when they come together in the non-solidified state, such that the direct drying subsequently is possible on a fluidized bed drier, the proposed process has the substantial disadvantage that hydrophobic silicic acid is used as the spray aid. The use of free silicic acid in the pharmaceutical or foodstuff industry, where further processing is carried out, is at least questionable, since it endangers health and is therefore not permitted for this purpose in many countries.
Therefore, the said process and the flowable dry particles of the aforementioned kind which are manufactured accordingly are not satisfactory, especially for use in the pharmaceutical or foodstuff industry.